A series of three yeast iso-1 cytochrome c derivatives will be prepared by covalent attachment of mercurialkylferrocenes to the sulfhydryl group of Cys-102 in the protein. These three protein derivatives will be characterized by chromatography cyclic voltammetry, iron and mercury analysis, thiol titration, peptide mapping, UV-visible, CD, and NMR spectroscopy. These cytochrome c-ferrocene derivatives will be prepared in the thermodynamically unfavored mixed oxidation state, i.e., either heme iron (II)-ferricenium iron(III) or heme iron(III)-ferrocene iron(II), by selective oxidation of the fully reduced derivative or by pulse radiolytic reduction of the fully oxidized derivative. The rates of intramolecular electron transfer within the protein derivatives will then be measured as a function of temperature. The reduction potentials of the ferrocenes to be used vary sufficiently to favor electron transfer from heme iron(II) to ferricenium iron(III) in some of the derivatives and from ferrocene iron(II) to heme iron(III) in derivatives prepared from the more reducing ferrocenes. This work would allow the measurement of the rate of intramolecular electron transfer both in and out of a native iron center at a fixed and approximately known distance for a series of very similar derivatives. It would also assess the influence of thermodynamic driving force on the rate of long-distance electron transfer since the potential differences between the two metal sites vary significantly across the derivatives to be studied. The significance of this work is that it will provide direct information on factors governing rates of electron transfer between distinct metal sites in multimetal proteins. In particular, this work addresses the dependence of such intramolecular electron transfer on: (1) intermetal distance, (2) nature of the intervening matter, (3) electron transfer free energy, (4) nature of the metal and its ligands, and (5) on temperature. An understanding of intramolecular electron transfer in these well-defined protein derivatives should markedly increase the understanding of intramolecular electron transfer in the native multimetal systems.